Electric cooking ovens

ABSTRACT

An electrically-heated heat-storage oven in which an oven liner of open-fronted box form is fitted externally with upper and lower sole plates which carry electrical heating elements and are backed by layers of refractory material. The refractory layers are built up from cast pieces of refractory material contained within sheet metal trays, the whole assembly being held together by upper and lower horizontal clamping beams connected to one another at their ends by spring-loaded vertical tie rods.

1451 May 1,1973

Unite States atent 1 91 Beech 1 ELECTRIC COOKING OVENS Inventor: Sydney George Beech, Sevenoaks,

England 8/1969 Harris,.lr........... 7/1966 Potenzo et a1.

4/1937 Dorl et a1. 11/1962 Mansfield Heat Limited, London, England Assignee:

c HS 4 6 9 1 8 22 Filed: Apr. 20, 1971 21 Appl.No.: 135,577

3/1965 Perl et a1.

Primary ExaminerVolodymyr Y. Mayewsky e Attorne --Dowell & Dowell Arthur E. Dowell Jr. 30 F A 11 t P 1 1) ta y 1 pp ca y a and Arthur E. Dowell, III

Nov. 27, 1970 Great Britainm....

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heating elements and are backed by layers of refractory material. The refractory layers are built up from 530540; 13/22 31 cast pieces of refractory material contained within sheet metal trays, the whole assembly being held together by upper and lower horizontal clamping beams connected to one another at their ends by spring-loaded vertical tie rods.

[56] References Cited UNITED STATES PATENTS 1,056,933 3/1913 Perkinsm................ ...219/394 3,059,087 10/1962 Perlman...............................2l9/394 7 Claims, 8 Drawing Figures Patented May 1,1973

6 Sheets-Sheet 5 Patented May1 ,197 3 v -3,731,039

6 Sheets-Sheet 4.

Patented May 1, 1973 6 Sheets-Sheet 5 Patnted May 1, 1973' 6 Sheets-Sheet 6 ELECTRIC CGOKING OVENS This invention relates to electric cooking ovens, and more particularly, is concerned with ovens of this kind in which provision is made for heat storage by the inclusion of slabs of heat-retaining material.

The technique of electrical heating with the use of refractory brick as a heat storage material is well known and proposals have previously been made for cooking ovens operating in this manner. However, the attainment of efficiency in such an oven necessitates a high internal temperature coupled with a low temperature at the outside of the stove or cabinet, and a correspondingly large differential thermal expansion. The problems of constructing an efficient heat storage cooking oven that also takes account of the thermal expansion difficulties have not hitherto been solved with entire success and it is an object of this invention to provide a better arrangement than has been available hitherto.

According to the present invention, a heat storage 7 electric oven has an oven box assembly comprising an oven liner fabricated in sheet metal, upper and lower sole plates outside the liner above and below it and contiguous with its top and bottom surfaces, electric heating elements assembled against the upper and lower surfaces of the upper and lower sole plates respectively, and refractory heat storage layers applied to the sole plates and covering said heating elements.

The refractory layers may be assembled from pieces of cast refractory brick, suitably channelled to fit over the heating elements, and contained within sheet metal trays attached to the sole plates. The preferred method of attaching the trays to the sole plates, and the sole plates in turn to the oven liner, is by means 'of top and bottom cross beams connected at their ends by spring loaded vertical tie-rods so that the various parts of the assembly are resiliently clamped together. This allows the parts freedom for differential expansion.

The oven box assembly may be supported on a main frame by means allowing limited horizontal movement. If a framing around the oven opening is sealed to the front of the oven liner, and this front framing has flanges which engage in front of front members of the main frame, the oven box assembly can be held by tension springs stretched betweenthe rear of the oven liner and back members of the main frame which springs will keep the assembly in position while again allowing freedom for differential thermal expansion.

One arrangement in accordance with the invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a pictorial view of the complete oven seen from the front;

FIG. 2 is a pictorial view of the oven seen from the back and with the outer cladding removed;

FIG. 3 is a pictorial view of the interior oven liner or box seen from the front;

FIG. 4 is a partial side elevation, partly in section, of the front framing of the oven liner;

FIG. 5 is a further pictorial view of the oven liner, seen from the front, with certain outer members assembled thereon;

FIG. 6 is a pictorial view of the oven liner seen from above, with sole plates, heating elements and refractory and sections assembled thereon;

FIG. 7 is a pictorial view of the oven liner, with the outer members assembled thereon, seen from the back, and

FIG. 8 is a pictorial view of the oven, with the outer cladding removed, seen from underneath and one end.

In the drawings, an oven box assembly 10 (FIG. 2) is supported on a welded frame 11. At the upper right hand front corner of this frame there is a mounting plate 12 for two manual control knobs 13, 14 (FIG. 1) and an associated fascia panel 15. The left hand control knob 13 is an on/off and oven heat control while the right hand knob 14 opens and closes a vent at the back of the oven. A main connection and switch box 16 (FIG. 2) is provided on the back of the frame 11 opposite the mounting plate 12 and the control operations are transmitted from the knobs 13, 14 to the connection box 16 by means of heat-insulated operating rods 17, 18 extending through from front to back. The fascia panel 15 also displays an on-off indicating lamp 1 9 energized by heat-insulated electric leads 20 extending to the front from the connection .box 16. .The oven has an interior lamp 21 which is switched on automatically when the oven door 22 is opened by means of a springloaded push-rod type control 23 protruding at the front of the frame and extending horizontally back to a switch 24 in the connection box 16. The interior lamp circuit has its own fuse 25.

The heat control knob 13 acts through the rod 17 to adjust the setting of a thermostat switch 26 in the connection box 16 which is connected to a thermostat phial 27 inside the oven-To protect the oven against damage in the event of failure of the inner thermostat phial, a second thermostat phial 28 is placed outside the oven near the bottom and against the back of the oven liner, this second phial being connected to a second thermostat switch 29 which is permanently set to open its switch contacts at a temperature above the normal working range of oven temperature determined by the thermostat switch 26. The vent control knob 14 acts through the rod 18 to operate a ball-jointed link 30 which is coupled to a crank arm 31 on a rotary crossrod 32 at the back of the oven. This cross-rod enters the oven vent pipe 33 and carries therein the disc 34 of a butterfly vent valve.

The oven is equipped inside with two wire shelves 35 (FIG. 1) running on adjustable shelf runners 36 that can be set at different heights. At the front is the door 22 which is a heat-insulated bottom-hinged door that drops down to form a platform to receive dishes being loaded into or removed from the oven. The oven door 22 has a full width handle 38 and is counterbalanced by springs 39 (FIG. 8) extending underneath the oven and anchored to the frame 11. The frame 11 (FIGS. 2 and 8) comprises corner uprights 40, front and rear top horizontal cross members 41, front and rear bottom horizontal cross members 42, top horizontal end members 43 and bottom horizontal end members 44. As well as these main members the frame has additional horizontal end members 45 near the top, additional vertical back members 46 and additional horizontal bottom members 47 extending from front to back, the members 46 and 47 being situated about a quarter of the distance in from the ends of the frame. The oven box assembly 10 is supported on the horizontal bottom members 47-. Around the oven box assembly, the frame 11 carries heat-insulating packing material and external panels 48 (FIG. 1).

The oven box assembly has an oven liner 49 which is fabricated from stainless steel folded sheets assembled by welding. This liner is heated by twelve hairpin form electrically-insulated electric elements 50 (FIGS. 2, 6 and 8) four of which are above the liner roof while the other eight are below the floor. Upper and lower aluminum sole plates 52, 53 (FIGS. 3 and 6) extend contiguously over the whole of the upper and lower outer surfaces respectively, of the oven liner 49. The electric elements 50 are housed in pockets formed by aluminum box section members 51 which are open at their rear ends and are spot-welded to the upper and lower surfaces, respectively, of the upper and lower sole plates. Upon the upper and lower surfaces, respectively, of the upper and lower sole plates there are placed layers 54, 55 (FIG. 6) of cast refractory brick assembled in sections and channelled to fit over the box section pockets 51. These brick layers are each onehalf inch thick and serve as heat storage material. The refractory brick sections are covered and retained by steel trays 56, 57 (FIGS. 5, 7 and 8). The sole plates 52, 53 are. located by tabs on the oven liner 49 which leave them free to expand over the liner surfaces.

The two assemblies each comprising a sole plate 52 or 53 and the associated heating elements 50, refractory brick 54 or 55 and retaining tray 56 or 57, are clamped against the top and bottom of the oven liner 49 by top and bottom cross beams 58 projecting beyond the oven liner and connected at their ends by vertical spring-loaded tie-rods 59 at each side of the oven liner. The front edges of the oven liner 49 are folded out and back to form a continuous channel section 63 (FIGS. 3 and 4) around the oven front opening. A framing 60 surrounds the oven front opening, the channel section 63 of the oven liner 49 being received within this framing and overlapping an internal flange 61 at the back of the framing 60 which flange lies immediately behind the channel section. To make a seal between the oven liner channel section 63 and the internal flange 61 on the framing 60 a filled P section woven glass fiber seal 62 is provided the stem of which is held clamped against the inner face of the outer channel section wall by an internal stainless steel clamping strip 64 and screws 65. The same screws 65 serve to secure the rear margins of thin stainless steel door sealing strips 66 to the outer face of the outer channel section wall by means of an external clamping strip 67. In order to accomodate the heads of the screws 65, the surrounding web of the oven front framing 60 is embossed to form in it a series of shallow circular wells 68.

When the oven box assembly is located within the main frame 1 1, external flanges 69 on the oven framing 60 are held against the front faces of from members of the main frame. The complete oven box assembly is supported on four ceramic bushes 81 (FIGS. and 8) and secured, in a manner allowing limited horizontal movement, to the members 47 at the bottom of the main frame 11. The method of assembly and fixing accomodates differences of expansion both vertically and horizontally in the various components with minimum distortion. Front to back variations in expansion rates are taken up by four tension springs 70 (FIGS. 2 and 81 connected between upper and lower rear edges of the oven liner and the vertical back members 46 of the main frame. The front channel section 63 of the oven liner 49, with its seal 62, is thereby pulled back and held firmly against the internal flange 61 of the oven front framing 60.

The whole of the space between the main frame 11 and the oven box assembly 10, supported on the main frame members 47 and located at the front by the framing 60, is packed with heat insulation in the form of mineral wool slabs in two layers some of which are shown in phantom at 160 in FIG. 5 with a sheet of reflecting aluminum foil 161 between the two layers. Similarly, the full-width oven door 22 (FIG. 1) contains two layers of slab heat-insulating material and an intervening sheet of reflecting foil. On its inner face the door 22 has an unfilled oven closure panel 71 of smaller area equal to the area of the oven front opening. The side edges of this oven closure panel are partly tapered or bevelled as at 72 so as to spread the door sealing strips 66 at the oven entrance as the door is closed. The door hinges on a full width hinge pin mounted within the door thickness upon brackets secured to and projecting from thefront of the main frame 11. The depth of engagement of the oven closure panel 71 and the door sealing strips 66, and the vertical alignment of the door and the oven, can be adjusted by adjusting the positions of the door hinge brackets on the main frame. The hinge pin is received in door hinge stride plates secured to the door 22 and these stride plates (FIG. 8) have arms connected to the door counterbalance springs 39 under the main frame 11 by means of Bowden cables 73 extending around pulleys 74 on the main frame.

What I claim is:

1. A heat storage electric oven, comprising a metal main frame, an oven box assembly supported on said main frame and including an oven liner fabricated in sheet metal which encloses an oven chamber, said oven liner having side walls, a top wall, a bottom wall and a back wall and open at the front, a heat-insulated closure door hinged on the main frame for closing the oven chamber front opening, external wall panels encasing said oven box assembly and main frame at the sides, top, bottom and back, heat insulating material interposed between said external wall panels and said oven box assembly, said oven box assembly further including upper and lower heat-conductive sole plates outside said oven liner above and below it and contiguous with its top and bottom surfaces, electrically-insulated electric heating elements assembled against the upper and lower surfaces of the upper and lower sole plates respectively, an electrical circuit for energizing said heating elements, electrically-insulating upper and lower refractory heat storage layers applied to said sole plates and covering said heating elements, upper and lower sheet metal trays containing said refractory layers, top and bottom cross beams clamping said trays to said sole plates and said sole plates to said oven liner, said cross beams having their ends projecting laterally beyond said over liner, and spring-loaded vertical tie rods connecting said top and bottom cross beams to one another at their laterally-projecting ends and allowing differential thermal expansion.

2. An oven according to claim 1, wherein the refractory layers are assembled from pieces of cast refractory brick, channelled to fit over the heating elements.

3. An oven according to claim 1, wherein the oven box assembly is supported on a main frame by means allowing limited horizontal movement.

4. An oven according to claim 3, wherein the oven box assembly includes a flanged front framing around the oven opening, which is sealed to the front of the oven liner, this framing having flanges that engage in front of front members of the main frame.

5. An oven according to claim 1, wherein said heating elements are of hair-pin form and contained in metal pockets attached to the sole plates.

6. A heat storage electric oven, comprising a metal main frame, an oven box assembly supported on said main frameand including an oven liner fabricated in sheet metal which encloses an oven chamber, said oven liner having side walls, a top wall, a bottom wall and a back wall and open at the front, a heat-insulating closure door hinged on the main frame for closing the oven chamber front opening, external wall panels encasing said oven box assembly and main frame at the springs connected between said over liner and back I members of said main frame to hold said oven liner in place while allowing differential expansion.

7. An oven according to claim 6, wherein the oven liner has an out-turned flanged portion around its front opening which engages in front of in-turned flanges on said front framing, a seal is interposed between said inturned flanges and said out-turned flanged portion, and the seal is clamped by the action of said tension-springs pulling back on said oven liner. 

1. A heat storage electric oven, comprising a metal main frame, an oven box assembly supported on said main frame and including an oven liner fabricated in sheet metal which encloses an oven chamber, said oven liner having side walls, a top wall, a bottom wall and a back wall and open at the front, a heat-insulated closure door hinged on the main frame for closing the oven chamber front opening, external wall panels encasing said oven box assembly and main frame at the sides, top, bottom and back, heat insulating material interposed between said external wall panels and said oven box assembly, said oven box assembly further including upper and lower heat-conductive sole plates outside said oven liner above and below it and contiguous with its top and bottom surfaces, electrically-insulated electric heating elements assembled against the upper and lower surfaces of the upper and lower sole plates respectively, an electrical circuit for energizing said heating elements, electrically-insulating upper and lower refractory heat storage layers applied to said sole plates and covering said heating elements, upper and lower sheet metal trays containing said refractory layers, top and bottom cross beams clamping said trays to said sole plates and said sole plates to said oven liner, said cross beams having their ends projecting laterally beyond said over liner, and spring-loaded vertical tie rods connecting said top and bottom cross beams to one another at their laterally-projecting ends and allowing differential thermal expansion.
 2. An oven according to claim 1, wherein the refractory layers are assembled from pieces of cast refractory brick, channelled to fit over the heating elements.
 3. An oven according to claim 1, wherein the oven box assembly is supported on a main frame by means allowing limited horizontal movement.
 4. An oven according to claim 3, wherein the oven box assembly includes a flanged front framing around the oven opening, which is sealed to the front of the oven liner, this framing having flanges that engage in front of front members of the main frame.
 5. An oven according to claim 1, wherein said heating elements are of hair-pin form and contained in metal pockets attached to the sole plates.
 6. A heat storage electric oven, comprising a metal main frame, an oven box assembly supported on said main frame and including an oven liner fabricated in sheet metal which encloses an oven chamber, said oven liner having side walls, a top wall, a bottom wall and a back wall and open at the front, a heat-insulating closure door hinged on the main frame for closing the oven chamber front opening, external wall panels encasing said oven box assembly and main frame at the sides, top, bottom and back, heat insulating material interposed between said external wall panels and said oven box assembly, said oven box assembly further including upper and lower heat-conductive sole plates outside said oven liner above and below it and contiguous with its top and bottom surfaces, electrically-insulated electric heating elements assembled against the upper and lower surfaces of the upper and lower sole plates respectively, an electrical circuit for energizing said heating elements, electrically-insulating upper and lower refractory heat storage layers applied to said sole plates and covering said heating elements, and tension springs connected between said over liner and back members of said main frame to hold said oven liner in place while allowing differential expansion.
 7. An oven according to claim 6, wherein the oven liner has an out-turned flanged portion around its front opening which engages in front of in-turned flanges on said front framing, a seal is interposed between said in-turned flanges and said out-turned flanged portion, and the seal is clamped by the action of said tension springs pulling back on said oven liner. 